This invention relates to the field of micromechanical devices, more particularly to spatial light modulator designs capable of performing analog pulse width modulation of image data using bistable micromirror devices.
A major advance in the design of spatial light modulators was the development of micromirror devices capable of operating in a bistable, or digital, mode. Digital operation of a micromirror device enables the use of digital pulse width modulation (PWM) and eliminates many of the manufacturing process dependent pixel-to-pixel variations that plagued analog-mode beam steering micromirror designs. Digital PWM operation, in which an analog voltage level representing the intensity of a pixel is digitized and each bit of the resulting word is displayed for a period proportional to its binary weight, comes at a tremendous cost in terms of data transfer rates and the hardware necessary to sample and process the image data.
PWM-based micromirror displays can create many image artifacts. These artifacts include motion and other artifacts caused by the digital nature of the display, as and artifacts caused by the differences between micromirror and CRT transfer functions. Motion artifacts are ameliorated by complicated processing of the digital data to strategically split many of the data bit periods into multiple bit periods which are then spread throughout the frame display period. Transfer function artifacts are reduced by removing the gamma compensation from the input signal.
The image data digitization and processing results in a very large amount of image data that must be loaded into the micromirror during a relatively short frame period. In addition to the high data rate required, the data must be reformatted from a pixel-serial, bit-parallel format to a pixel-parallel, bit-serial format. This xe2x80x9ccorner turningxe2x80x9d function provides equal weight image data bits for many pixels for each display period.
What is needed is a method and system of operating a digital micromirror device that does not require the image processing hardware and memory necessary to perform digital PWM.
Objects and advantages will be obvious, and will in part appear hereinafter and will be accomplished by the present invention that provides a method and system for analog pulse width modulation of a digital micromirror device. One embodiment of the claimed invention provides a method of operating a bistable micromirror array. The method comprises the step of providing a data signal to address circuitry in each cell of the bistable array, the data signal representative of the desired intensity of a pixel formed by the micromirror cell, which is a function of the position of the deflectable mirror element integrated over a field or frame period. A ramp signal is provided to the address circuitry in each said cell and a mirror address signal dependent on the difference between said data signal and said ramp signal is generated. A bias signal is also provided to the addressing circuitry. The bias signal and mirror address signal cooperative operate to deflect the mirror element to a first position when the address signal is equal to a pre-charge value, and a second position when the address signal is equal to the ramp voltage.
The disclosed addressing circuitry and method provides a method and system for controlling a micromirror display system that requires a minimal amount of control hardware. The method also eliminates the artifacts created by various forms of digital pulse width modulation. Thus, the method and system enable a low-cost display system to provide an acceptable image.